Nuclear electrical generator



Dec. l, 1953 E G UNDER 2,661,431

NUCLEAR ELECTRICAL GENERATOR Filed Aug. 3, 1951 INVENTOR Elgzw .Linder ATTORNEY Patented Dec. 1, 1953 UNITED STATES OFFHCE NUCLEAR ELECTRICAL GENERATOR Ernest G. Linder, Princeton, N. J., assigner to Radio Corporation of America, a corporation of Delaware 1 Claims.

This invention relates generally to the generation of electrical energy and particularly to improved methods of and means for deriving and utilizing the electrical energy of nuclear reactions.

The enormous magnitudes of energy provided by certain nuclear reactions of radioactive substances provide a tremendous field for the development of new sources of electrical energy. Since some radioactive radiations (energy) are largely electrical in nature, it is desirable that such electrical energy be converted directly to electrical energy of usable form. The alphaparticle and beta-particle emissions from certain radioactive substances comprise positively or negatively charged particle rays, respectively vhaving energies which vary from low values to iseveral million electron volts.

For example, alpha-ray emission comprises positively charged particles having energies varying from zero to the order of ten million electron volts, While beta-particle emission comprises negatively charged particles having energies varying from low values to the order of three million electron Volts. Different radioactive substances are known to provide either alpha-particle emission, beta-particle emission, or a combination of alpha-particle and beta-particle emission. The direct utilization of the high electrical potentials which may be derived from such charged particles provides much more convenient and eicient utilization of nuclear energy than previously proposed systems wherein the nuclear energy is converted to thermal energy, the thermal energy converted to mechanical energy, and the mechanical energy then converted to electrical energy in a usable form. Also the direct utilization of the electrical energy of nuclear reactions may be much more readily controlled by electrical methods than may the conversion of nuclear energy to thermal energy.

The instant invention is an improvement over the devices disclosed in applicants U. S. Patent .2,517,120, filed June 25, 1946, granted August 1,

1950. Said patent discloses the use of collector electrodes for collecting the charged particle rays from a radioactive source, and means for apply- -ing the resultant unidirectional potential between the source and collector electrodes to a load.

One of the factors which greatly limits the eiciency of all radioactive generators is the absorption Within the radioactive material itself of particles emitted from the interior thereof.

"The instant invention utilizes improved emitting j and collecting structures comprising substantialiy equi-spaced sheet-like emitting and collecting electrodes separated by charged particle permeable insulating means which support the elements in said equi-spaced relation.

A rst embodiment of the invention employs a plurality of alternately arranged emitting and. collecting sheet electrodes separated by suitable insulating spacers, the several emitters and collectors being' respectively connected in parallel to common load terminals, the entire assembly being supported Within an evacuated enclosure.

A second embodiment of the invention employs a structure similar to the rst embodiment with the exception that the emitting and collecting electrodes are effectively connected in series to provide an output voltage dependent upon vthe number of series-connected sections.

A third embodiment of the invention employs a pair of emitting and collecting sheet electrodes arranged in a spiral, the adjacent electrode portions being separated by suitable insulating spacers. The latter structure has the advantage that relatively large active surface areas may be incorporated in a compact unit.

One oi the objects of the invention is to provide improved and more eiiicient methods of and means for generating electrical energy in response to nuclear reactions.

Another object is to provide improved and more efficient electrode structural arrangements for utilizing the electrical energy in nuclear reactions for generating high unidirectional potentials.

An additional object is to minimize the internal absorption of radioactive emission in the emitter material of nuclear generators.

A further object is to provide improved means for converting atomic energy directly to electrical energy in commercially usable forms.

The various embodiments and features of the invention Will be described in greater detail hereinafter by reference to the accompanying drawing of which Fig. 1 is a schematic diagram of a first embodiment of the invention having a plurality of emitters and collectors connected in parallel; Fig. 2 is a schematic diagram of a second embodiment of the invention having a plurality of emitters and collectors connected in series; and Fig. 3 is a schematic diagram of a third embodiment of the invention having the collectors and emitters in a spiral arrangement.

Y Similar reference characters are applied to simitively until it reaches a potentialsiently.high

to repel additional alpha particl si. In such/a modification of the inventidn,"the 'olle'ctor elec?.

trode becomes the positive'A terminal and the radioactive source the negative terminal of the generator.

The electric current produced by any source of charged particles is fe-e- Where n is the number of particles emitted, t is the time in seconds, and therefore {ln/dt is the rate of particle emission, and e i`s the .electrical charge per particle. If each particle carries more than one electronic charge, e must be replaced by ne, where ,a is the numbernof charges.

For a radioactive substance (2) cin/dt: -,\n

(seeV Pollardand ,Davidson Applied Nuclear Physics, p. 105) v vherek ,is thedecay constant and is related to the half life in by From Equationsil, antifa*Y itis seen that .i 0.693 (4) z-yen H The number `of;after-ns1.contained.in a substance of mass M and atomic Weight A is F (D) n- MHA Where me is the mass of the hydrogen atom.

Thus M This relation may be' expressed in amperes per gram for a predetermined quantity of a radioactive substance wherein e=1.59 l19 coulombs, M=1 gram, mHiL66 1G24 grams, and tn=8-4 104TH,V where TH is the half life in days. Therefore,

If the radioactivesource i's polonium, 4:'210 and T11-1140, ii=2, therefore =51.s i0-,6 ames/gram 51.8 microamps/gram The characteristics of' the changeal particle emitting substance determ'ine not only the output voltage of the generator, but also determine its impedance. Thus, `since alpha particles generally havever'y'uniforin energy'pr'oviding the source is 'a very thin element, the generated voltage would -`remain substantially constant until au the remaning'cuifent 'was' drawn; whereupon vthe voltage would Ydecrease rapidly. Thus; with an alpha-particle emitter, the generator would have a low effective internal impedance. In oontradistinction thereto, beta particles are usually emitted over a Wide energy range which may vary from a very 10W value to several million electron volts. Consequently, when current is ldravvn from the generator to a load, the load voltage would immediately drop to a much lower value than the no load maximum, as is characteristic of all generators having high interial impedance. The actual variation of load voltage with current would depend upon the particular characteristics of the beta-ray emittingpmaterial. general the available powei depehd'suponthe quantity of radioactive material einployedA and upon its rate of particle emission. Materials which emit at high rates have short operating life, while materials emitting at low rates have relatively longer operating lives. In general, generators Aof the types d lesrcribedV have particular application for systems requiring, high voltage and low power ca;- pacity since in such instances only a relatively small amount of radioactive material is required for the alpha- `orbeta-ray source. 4,

Following is apartial list of alphaand betaray emittersfwhich are suitable for high voltage generators of the types described heretofore:

ALPHA-RAY EMITTERS Encigly e uiva cnt Element Hlf'he Cilnillic'n nys electron volts) Polonum (Po 210) 5. 30 Actini'uln (Ac 223) l1.2 6. 72 ThoriuuiX ('lh X 224) 8. 64 5. 68 Radio actinium (Rd Ac 227) 13. 5 5. 00

BETA-RAY EMITTE RS Phosphorus (P 32) 14. 30 l. 72 Calcium (Ca 45) 180 0. 25 Scandium (Sc 4r") 85 0. 3G Iron (Fe 59) 47 0. 26 o. 46 Arsenic (As 74,) 16 1. 3 Strontium (Sr 59) 54 l; 5 Strontium (Sr` QD) 1 25 0.60 Aiiti'mol'ly (Sb 124,) 60 2. 4 Cerium (Ce 144).. 275 0. 35 Tungsten (W 1E5) 77 0. 675

1 Years. n l

Referring to Fig. l of the drawing, the rst embodiment of the invention includes a plurality Vof radioactive emitters! cooperating with a plurality of Aemission collecting electrodes 3 and spaced therefrom? by a plurality of charged particle'A` pernfieable,Y such as open mesh, insulators 5 al1 enclosedA Within an evacuated enclosure 1. All ofthe emitters I arelconnected together and brought out through the evacuated enclosure through an output lead '9'. Similarly, v'all of the collectors are collected together and broilglipt out through a second o ut- 'put lead Il. The output leads 9 and Il are connected to any desired load l 3.

conducting material suiciently thick to stop substantially all alpha-ray or beta-ray radiation, as the case may be. Electrodes of 3 millimeter thick iron would be suitable. The open mesh insulator may comprise a polystyrene mesh of sufcient thickness to provide the desired spacing and insulation breakdown characteristics between the emitters and the collectors. The appropriate spacing provided by the insulating meshes 5 will depend upon the load impedance which will determine the average output voltage. Since a plurality of relatively large area emitters and collectors are relatively connected in parallel, the output current derived from the embodiment shown in Fig. 1 may be as much as one thousand times greater than would be obtainable from the same quantity of radioactive emissive material concentrated in a compact volume as described in applicants patent identified heretofore.

The second embodiment of the invention shown in Fig. 2 utilizes a plurality of series-connected emitters and collectors providing a much higher output load voltage with correspondingly lower maximum load current. In this embodiment of the invention the emissive material l is coated upon one surface of the relatively heavy collector electrodes 3. The radioactive emission from each emitter I is collected upon the adjacently disposed surface of the next collector electrode 3 which is spaced from the first emitter by a mesh insulator 5 as described heretofore. Thus the voltage generated between successive emitters and collectors is additively combined to provide an extremely high output load voltage.

In both of the embodiments of the invention I illustrated in Figs. 1 and 2, the relatively thick absorbing collector electrodes prevent interaction between the several emitting electrodes which would tend to discharge the device internally.

A particularly encient and compact modica- /A tion of the first embodiment of the invention is shown in Fig. 3. This device comprises a thin foil of aluminum or other conducting material having radioactive emissive material coated in a thin layer on both surfaces thereof. Alternatively, the radioactive material may comprise a thin layer disposed between two extremely thin conducting foils as described heretofore in Eig. l. An adjacently disposed, relatively thick, emission-absorbing collector 5 having the same, or slightly larger, area as the emissive electrode is separated therefrom by a suitably proportioned mesh insulator 5. The whole assembly is formed into a spiral cylinder and enclosed within an evacuated envelope, not shown. Thus the radioyand relatively low current.

What is claimed is:

1. Apparatus for primarily generating electrical energy including an evacuated envelope containing a plurality of emitters comprising radioactive material providing charged particle cold high energy emission, a plurality of collector electrodes alternately interspersed between and closely juxtaposed with said emitters, said emitters and collector electrodes comprising effectively equi-spaced sheet-like elements, insulating means substantially permeable to said emission for supporting said elements in said equi-spaced relation, and means connected to said elements for deriving a load current.

2. Apparatus according o claim l wherein said emission from each of said emitters is collected on one of said collector electrodes.

3. Apparatus according to claim l wherein said emission from each of said emitters is collected by a plurality of said collector electrodes.

4. Apparatus according to claim 1 wherein said collector electrodes are substantially opaque to said emission.

5. Apparatus for primarily generating electrical energy including an evacuated envelope containing a plurality of emitters comprising radioactive material providing charged particle cold high energy emission, a plurality of collector electrodes alternately interspersed between and closely juxtaposed with said emitters, said emitters and collector electrodes comprising eiTectively equi-spaced sheet-like elements, insulating means substantially permeable to said emission for supporting said elements in said equispaced relation, and separate means respectively shunt connected to said emitters and to said collector electrodes for deriving a load current.

6. Apparatus for primarily generating electrical energy including an evacuated envelope containing a plurality of emitters comprising radioactive material providing charged particle cold high energy emission, a plurality of collector electrodes alternately closely interspersed between and closely juxtaposed with said emitters, said emitters and collector electrodes comprising effectively equi-spaced sheet-like elements for establishing incremental potentials, insulating means substantially permeable to said emission for supporting said elements in said equi-spaced relation, and means connected to said elements for combining said incremental potentials for deriving a load current.

7. Apparatus according to claim 6 wherein each emitter comprises radioactive material disposed upon a single face of one of said collector electrodes, said emitter being insulated from the next adjacent one of said collector electrodes.

ERNEST G. LINDER.

References Cited in the le of this patent Publication: A New Electronic Battery. The Electrician, October 31, 1923, page 497.

Publication: A New Type of Electrostatic Generator. Miller, Physical Review, vol. 69, Nos. 11 and 12, June 1946, page 666.

Publication: Nuclear Electrostatic Generator, Linder, Phy. Review, vol. 71, No. 2, pp. 129-130, 

